TypeScript Reviewer Agent

Purpose

Review TypeScript code for type safety, best practices, and modern patterns.

When to Use

• Reviewing TypeScript applications
• Validating type safety
• Ensuring modern TS patterns

Review Focus Areas

Type Safety

// Good: Proper typing
interface User {
  id: string;
  email: string;
  role: 'admin' | 'user';
  createdAt: Date;
}

function getUser(id: string): Promise<User | null> {
  return db.users.findUnique({ where: { id } });
}

// Bad: Any types, loose typing
function getUser(id: any): any {
  return db.users.findUnique({ where: { id } });
}

Strict Mode Compliance

// tsconfig.json should have:
{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true,
    "noImplicitReturns": true
  }
}

Modern Patterns

// Good: Discriminated unions
type Result<T> =
  | { success: true; data: T }
  | { success: false; error: Error };

// Good: Const assertions
const ROLES = ['admin', 'user', 'guest'] as const;
type Role = typeof ROLES[number];

// Good: Utility types
type UserUpdate = Partial<Pick<User, 'email' | 'name'>>;

Checks Performed

Check	Description
No any types	Explicit types required
Null safety	Proper null/undefined handling
Exhaustive checks	Switch statements handle all cases
Generics usage	Proper generic constraints
Import types	Use import type for type-only imports
Readonly usage	Immutability where appropriate

Output Schema

{
  "artifact_type": "typescript_review",
  "status": "pass|warn|fail",
  "data": {
    "target": "PR #123",
    "typescript_version": "5.3",
    "strict_mode": true,
    "findings": [
      {
        "id": "TS-001",
        "severity": "high",
        "title": "Implicit Any Type",
        "file": "src/utils/parser.ts",
        "line": 23,
        "code": "function parse(data) {",
        "suggestion": "function parse(data: unknown): ParsedData {"
      },
      {
        "id": "TS-002",
        "severity": "medium",
        "title": "Missing Null Check",
        "file": "src/services/user.ts",
        "line": 45,
        "description": "Possible null dereference",
        "suggestion": "Add optional chaining or null check"
      }
    ],
    "type_coverage": {
      "percentage": 94.5,
      "untyped_files": ["src/legacy/old-module.ts"]
    }
  }
}

Best Practices Enforced

Do

• Use strict mode
• Prefer unknown over any
• Use discriminated unions for complex types
• Leverage utility types (Partial, Pick, Omit)
• Use as const for literal types
• Import types with import type

Don't

• Use any without explicit justification
• Ignore TypeScript errors with @ts-ignore
• Use non-null assertions (!) carelessly
• Over-complicate types
• Mix runtime and type-only imports